GhostRider62

Jan Heine claims a 12% increase in power for a more flexible steel bike compared to a less flexible one. He does not show his work or the data. He shows a chart and says his legs feel warm on one bike and they hurt on the other. He claims the power meters were calibrated, by whom? Where is the cert. IIRC, there was a BQ article or two on the Specialized Diverge and it climbed better than his flexy steel bike but I could be wrong, I threw out all my BQ magazines and ended the subscription at that point. He measures speed with a GPS device to make conclusions on comparative tests. Real scientifically.

I also do not recall any explanation why the Diverge climbed better than his steel bike. Also, Lael Wilcox rides a Diverge and I tend to look at what top riders like she use more than marketing pieces.

I'd like to see one other "study" making the claim that a 0.4 mm tubing steel bike flexy as a noodle makes 12% more power.

That is really the gist of this thread. If lateral stiffness at the BB and chainstays did not matter, all those Specialized, Trek, Cervelo engineers need to be fired.

Milton Keynes

Yeah, I don't know, I'll just leave all this scientific physics talk to those who want to argue over it and just get on my bike and ride. While you guys can think about how the springiness of your frames are affecting your power curve, I'll just ride along and think things like, "Oh look! Cute bunny!"

So I guess the OP is correct, stiffness of my frame doesn't matter because I never think about it. I just got sucked into this thread by the double entendre.

GhostRider62

The question of rigidity or flexibility is complicated. Some bikes have brutally stiff seat stays. This was the reason I bought the cheaper 2016 Cervelo S3 instead of the S5 at the time. The S3 had the stays from the R5 essentially but the downtube of the S5. Best of both worlds. Stiff downtube and chainstays = good. Stiff seat stays = bad. Top tube = ?

I find it hard to enjoy the bunny rabbits when my butt is being pounded. The best modernish bike that I rode was a Felt AR1, the BB was stiff enough and it was comfortable for a racing bike. Maybe a lighter rider would have had a different impression. When buying a bike, this is kind of an important consideration.

My noodle Vitus in the 80's was so flexible that I could shift gears stomping on the pedals. But many people thought those bikes climbed well, I might have been too heavy (168 lbs on a 60 cm frame). It also shimmied violently at speed. Fun.

Kapusta

Whether or not stiffness matters for efficiency, it can make a difference in handling and tracking. This is a big factor in mountain bikes, but I think it is also true to some extent for road bikes.

Regarding the effects on pedaling, in particular out-of-saddle efforts....

I don’t think anyone can deny that out of the saddle hammering on a stiff vs flexible frame feels different. So clearly something is different. Until you can fully explain WHY it feels different and give an explanation as to why that does not in fact matter, then you cannot categorically assert that stiffness does not matter.

Maelochs

He can assert any danged thing he wants .... demonstrably so.

https://www.tfes.org/

GhostRider62

Interesting comments about frame and wheel stiffness by Damon Rinard in the attached.

I can only imagine the vertical compliance comfort of a newer bike with seat stays attached halfway down the seat tube and a flexible seat post. Tour Magazin is the only one I know who systematically measures vertical and horizontal deflections. Minimizing vertical deflection is important because human tissue does not plane, it absorbs the energy and this also contributes to fatigue.

https://cyclingtips.com/2018/04/jra-...-still-matter/

Flip Flop Rider

is it winter already?

livedarklions

Your last paragraph is a clever burden shift--nobody can prove that a non-defined parameter doesn't matter. That has absolutely no implication that the "feel" matters in any way related to performance. And feels different = is different is actually a non sequitur. People "feel" like they're going faster when they can perceive bumps, and interpret smoothness in ride as going slower even if there is no difference in speed from the bumpier ride.

GhostRider62

Many riders feel that tires are faster went pumped to the maximum. I don't feel the onus to provide data describing their feelings or other emotions.

All of my fastest climbing bikes have always been stiff at the BB. You know like objectively. Always the fastest up the same climb. Is that because I am a big rider and like to climb in the big ring? Please show your data and calculations.

63rickert

In original post there is an assertion that stiffness does not matter for the racks mounted on a bike. Because if they weren’t stiff enough they would break. Umm, racks do break, they break all the time. Current custom builders are using bigger diameter and stiffer tubes than ever previously in the history of bikes. In hopes they won’t break. This would include custom builders who are still using 1” and 1-1/8” frame tubes.

Second post brings up stiff versus sagging car doors. ???? Car doors sag because of wear and free play in the hinges. A stiff car door would be one that required some force to make the hinge move.

Discussion of bicycle stiffness is normally continuous non sequiturs.

The Eddy Merckx hour record, still unbeaten after 49 years, was done on a Colnago built with Reynolds 22/28 butted tubes. In old style skinny diameter. Converting British wire gauge to metric gives wall thickness of 0.711/0.376mm. Of course Reynolds never produced anything accurate to 0.001mm, that is just how the nominal converts. But the skinny belly of the tube was less than 0.4mm. Every Category 6 rider knows that such a frame is impossibly flexible and noodly. What was good enough for Eddy would be laughed out of current market. When you can put out 750-800 watts continuously for an hour get back to me.

Maelochs

Except, of course, that flexibility on a track and in steady-state riding (even at massive power output) is nothing at all like road riding---smooth track, smooth pedalling, minimal longitudinal acceleration ...... nothing like sprinting, or climbing at max power ..... so your data input is a meaningless as anyone else's.

So far this whole thread is basically, "Yes, because I said so .... No, because I said so" repeated continually.

By the way ... maybe if he had been riding a modern Merckx bike that hour record would be significantly faster.

PeteHski

Lateral stiffness definitely matters for a number of reasons, just not in the way being touted on this thread in relation to power being "lost" through frame flex. The frame loading is relatively low (human power is feeble) and the hysteresis losses in flexing the BB and chainstays are tiny in absolute terms before even comparing differences between various frames. Frame stiffness is all about handling response, stability and comfort. The main parameters in play here are lateral stiffness, vertical stiffness and torsional stiffness. You can definitely make a frame too stiff vertically (harsh riding), the other two are more debatable, but stiffer is generally better unless you make it excessively heavy.

Kapusta

Making a categorical statement carries with it a high burden of proof.

The OP has stated categorically that stiffness does not matter. Period. And this assertion is based solely on the idea that there is no difference in efficiency. What I am challenging is this idea that same efficiency = no difference.

I did not say that since pedaling a flexible frame feels different that it is in fact less efficient. (Defined strictly
by power into the pedals vs power out in the wheels). What I said was that it is in some way different.

Just because two systems ultimately have the same efficiency (power in vs power out) does not mean that we as biological creatures are always able to deal equally well with them.

Take the example of gearing. Strictly speaking there is essentially no difference in the efficiency of a higher vs lower gear. Does that mean it does not matter what gear you are in?

Introducing a spring into a system absolutely changes the way we interact with it. And that is immediately evident in how it feels. In fact, how something feels is often one of the best indicators that there is a spring somewhere in the system, be it in pedaling, braking, or pulling on the handlebars.

I think your tire pressure analogy is off base, here. Are you suggesting that tire pressure categorically makes no difference? Tire pressure is probably a perfect example of when one should NOT be making categorical statements.

Where I think you and I may be in agreement is that one should not assume that they know exactly what their subjective experience is caused by or indicates. People should not assume that the harsher ride of an over inflated tire is faster. And people should also not assume that the flex they are experiencing in a bike means that the bike itself is less efficient.

PeteHski

I agree with this. IME of race car engineering a lot of drivers have a tendency to set up their cars way too stiff based on subjective “feel”. Often going softer on springs, anti-roll-bars and damping improves both traction and lateral grip. Drivers are often surprised by the stopwatch vs perception. Especially in low-downforce formula like Touring Cars where aero performance is much less critical.

Trakhak

Merckx's record (49.431 km) has been beaten twice:

Chris Boardman, Manchester, 27.10.2000, 49.441 km
Ondrej Sosenka, Moscow, 19.7.2005, 49.700 km

Sosenka and his bike:

Maelochs

Dude, there is a time and a place for facts, and this isn't it, ever.

tomato coupe

Yep, facts just cloud the issue.

livedarklions

Well, if you rewrite my post to refer only to efficiency and tire pressure (neither of which I mentioned), fine. I actually referred to "performance" and "perceiving bumps".

I'm skeptical that your "feeling" is as accurate a way to detect springing as you assert. It would be interesting to see if there's a way to blindfold test this.

To be honest, I really have no dog in this fight because I haven't found stiffness to matter much for feel or speed in road biking and tend to think if you find you prefer to ride a stiffer bike, it really isn't up to me whether that subjective taste is rational or not.

Ultimately, this is a "you shouldn't care about the things you care about" thread with just a smidgen of data, and I should know better than to stick my nose into one of those pointless debates.

PeteHski

You can definitely argue in favour of more vertical frame compliance. In fact many manufacturers already have. That's why we have super thin seat-stays, D-shaped seat posts, IsoSpeed, Futureshock, etc. Wider tyres and lower pressures have arguably made frame compliance much less critical in very recent years, but still I'd rather not have a bone-shaking stiff frame for riding on our pot-holed roads. CF goodness can give you vertical compliance and high lateral stiffness at the same time.

63rickert

OK. With flattish rims and full spoke count. I did not know that and I thank you.

63rickert

Merckx did first kilo in 1:12. Try doing that, then tell me about steady state riding. Would also note here that for the way he was trained and the way racers rode back then Merckx was massively overgeared to be accomplishing such a quick first kilo.

HTupolev

No. The claims around "planing" are not at all explained by a description for why losses might be minimized. "Planing" is a notion that requires frame flex to affect the output at the riders' legs, and any explanation for it will probably require a biomechanical element.

This said, I do think that there's some reality behind Heine's observations. While his study was somewhat crude, and it did not sample a wide variety of flex characteristics nor very many riders (making it extremely hard to generalize or draw any practicable conclusions from), it is suggestive that something interesting is happening.
And I've had experiences that mirror his with regards to frames pedaling badly. A couple years ago I borrowed a friends' circa-2013 Pinarello Paris for a while, and my legs just didn't get along with it: it felt stiff, but the stiffness was less "rocket ship" than "kicking a brick wall." It was like I couldn't keep my pedal stroke engaged correctly with the cranks at my desired rhythm, my performance and self-selected cadence suffered even though my cardio had no trouble keeping up.

GhostRider62

Who needs logic with obvious errors of fact.

1. The record has been broken
2. The bike used Columbus tubing
3. The power was not close to 750-800 watts. He might have needed 400 watts at that altitude.

ChamoisDavisJr

But Merckx was jittered up on Amphetamines making it harder to ride in a straight line. Let’s see these young fellas do that!

Merckx is steel the best

livedarklions

Will a stiff drink get you drunker faster than a strong drink?

I don't think that one runs afoul of the unterhausen rule on this thread, right?